1 Field of the Invention
The present invention relates to a fixing device for an image forming apparatus using an electrophotographic method for use in copying machines and printers.
2. Description of the Related Arts
Conventional fixing devices in image forming apparatus employing an electrophotographic method and used in copying machines and printers are installed within the bottom unit [a] of the copying machine, wherein a movable frame [c] which supports a heating roller [b]is forced upward relative to a stationary frame [e] which supports a pressure roller [d], as shown in FIG. 8. When the top unit [f] is raised from the closed position indicated by the imaginary lines in the drawing to the open position indicated by the solid lines to process a paper jam, movable frame [c] pivotally moves in an upward direction as it is released from the pressure applied by pressing portion [h] of top unit [f] to passive portion [g] at the free end of said frame [c]. The aforesaid action results in heating roller [b] being separated upwardly from pressure roller [d]. Thus, the transfer sheet [i] which is jammed in the fixing portion is freed from the grip between both rollers [b] and [d] and can thereby be readily removed.
Recent copying machines continue to be down-scaled in size, and fixing devices are designed to be as compact as possible. Thus, even when the heating roller [b] and pressure roller [d] are separated, jammed transfer sheet [i] is often extracted from the less troublesome discharge sheet side.
However, unfixed toner [j] remains on the portion of said sheet [i] on the upstream side of both rollers [b] and [d] in the sheet feed direction and when extracting a jammed transfer sheet [i] in the aforesaid manner, said unfixed toner [j] adheres to the surface of the heating roller [b] when transfer sheet [i] comes into contact with heating roller [b]. The aforesaid adhered toner [j] is transferred to the transfer sheet [i] during the next fixing process, thereby soiling the surface of said subsequent transfer sheet [i]. Further, when the jammed transfer sheet [i] extends only slightly downstream from both rollers [b] and [d] in the sheet feed direction, the hand of the operator used to extract said jammed sheet comes near to heating roller [b] and is exposed to the danger of making contact with said heating roller [b].
A fixing device has been proposed wherein a roller to prevent the transfer sheet from rising when said sheet is pulled out is mounted to a stationary frame to prevent the jammed transfer sheet from making contact with the heating roller.
However, because the aforesaid roller is disposed immediately above the sheet feed path of the fixing device on the upstream side of the aforesaid heating roller and pressure roller, as viewed from the sheet transport direction, said roller, rather than being an aid, quite to the contrary actually hinders the travel of the sheet and increases the probability of a jam. The aforesaid roller causes further inconvenient when trying to grasp the sheet from the sheet discharge side so as to extract the jammed sheet if said jammed sheet extends slightly downstream from the heating roller and pressure roller in the sheet transport direction. Even when the jammed sheet can be grasped and extracted as described above, it is difficult to accomplish the removal while avoiding contact of the sheet with the aforesaid roller, and unfixed toner which comes into contact with the aforesaid roller is loosened and falls into the device, thereby causing another disadvantage. When the jammed sheet extends slightly downstream from the heating roller and pressure roller in the sheet transport direction, the hand of the operator used to try and remove the jammed sheet comes near to the heating roller and is exposed to the danger of making contact with said heating roller.